1. Field of the Invention
This invention relates to a light-emitting material containing a nano-phosphor, a light-emitting element using the same and a method of manufacturing the same.
2. Related Background Art
Flat panel displays (FPD) realized by using phosphor thin films and phosphor powders having a light-emitting effect have been and are attracting attention. Flat panel displays include plasma displays (PDP), field emission displays (FED) and, electro-luminescent displays (ELD). Such phosphors that are used for displays of a specific type are required to match the characteristic features of the displays.
Phosphors that have been prepared are conventionally produced by adding one or more than one transition metals and/or one or more than one rare earth elements as luminescent center to oxides or sulfides as matrix. Examples of known phosphors for inorganic EL include ZnS:Mn, SrS:Ce,Eu, CaS:Eu, ZnS:Tb,F, CaS:Ce, SrS:Ce, CaGa2S4:Ce, BaAl2S4:Eu, Ga3O3:Eu, Y2O3:Eu, Zn2SiO4:Mn and ZnGa2O4:Mn. Examples of other phosphors that have been prepared include Y2O2S:Eu3+, Gd2O2S:Eu3+, YVO4:Eu3+, Y2O2S:Eu,Sm, SrTiO3:Pr, BaSi2Al2O8:Eu2+, BaMg2Al16O27:Eu2+, Y0.65Gd0.35BO3:Eu3+, La2O2S:Eu3+,Sm, Ba2SiO4:Eu2+, Zn(Ga,Al)2O4:Mn, Y3(Al,Ga)5O12:Tb, Y2SiO5:Tb, ZnS:Cu, Zn2SiO4:Mn, BaAl2Si2O8:Eu2+, BaMgAl14O23:Eu2+, Y2SiO5:Ce and ZnGa2O4:Mn.
Inorganic EL displays are among the displays that are attracting attention because polycrystalline inorganic phosphors can be used for them to provide a large display area with relative ease and they show an enhanced durability in the operating environment. Efforts for developing full color EL displays that utilize in organic EL have been paid in recent years although no highly efficient phosphor showing a high degree of color purity and a high luminance level has so far been obtained. Therefore, it is indispensable to develop a high performance phosphor in order to realize a full color inorganic EL display.
Meanwhile, the light-emitting characteristics of very small particles of semiconductors such as Si, Ge and II-VI compounds having a diameter not greater than tens of several nanometers that are attributable to the quantum size effect have been made clear in recent years. The quantum size effect is believed to be derived from the fact that very fine particles of semiconductors with nano-crystal structure have a band gap greater than that of bulk semiconductors. As a remarkable example, it has been observed that light emitted from CdSe semiconductor fine particles tends to show a shorter wavelength as the particle diameter is reduced. Additionally, light emitted from semiconductor fine particles shows a high luminance level because their light-emitting life is very short and not longer than 10 ns and light is absorbed and radiated in a very short period of time.
Very fine particles of semiconductors as described above can be produced in an aqueous solution (Journal of Physical Chemistry, B, Vol. 102, p. 8,360 (1998)). A technique for fixing very fine particles of a semiconductor generated in an aqueous solution to a solid matrix of a polymer has been proposed (Advanced Material, vol. 12, p. 1,103 (2000)). However, since polymers are poorly resistant to light and heat, the very fine particles fixed to polymers may easily become degraded.